Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides

Kiumars Aryana; Derek A Stewart; John T Gaskins; Joyeeta Nag; John C Read; David H Olson; Michael K Grobis; Patrick E Hopkins

doi:10.1038/s41467-021-22999-z

Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides

Nat Commun. 2021 May 14;12(1):2817. doi: 10.1038/s41467-021-22999-z.

Authors

Kiumars Aryana¹, Derek A Stewart², John T Gaskins¹, Joyeeta Nag², John C Read², David H Olson¹, Michael K Grobis², Patrick E Hopkins^{3

4

5}

Affiliations

¹ Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, USA.
² Western Digital Corporation, San Jose, CA, USA.
³ Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, USA. [email protected].
⁴ Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA, USA. [email protected].
⁵ Department of Physics, University of Virginia, Charlottesville, VA, USA. [email protected].

Abstract

Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10 ± 0.01 W m^-1 K^-1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network.